Altoids Tin 1/8" Stereo Mixer

Step 14 Final Comments

It may look strange to build an electronics project without a circuit board in this open wiring style. Old timers called it "rats nest" wiring, but despite the negative term it's perfectly OK.

If you construct it right, the wiring has enough strength to stand on its own and the box provides adequate shielding.I've used my mixers in the car and elsewhere with no problems for several years.

However, if you're worried about the open wiring, then you can always cover the bare wires & resistors with electricians tape, just make sure not to break something in the process. 

If you really wanted to make the mixer super rugged, you could fill the tin with epoxy, parafin or circuit-grade Silicone RTV.

Note: Don't use the regular Silicone RTV made for caulking and bathroom sealer. This stuff gives off acetic acid which will eat through your wires and ruin your project after a while. Circuit-grade Silicone RTV does not give off acid and is safe for wiring. I've read that GE Silicone II (available at home improvement stores) does not leach acid and also silicone RTV sold at automotive part stores labeled either 'Oxygen-sensor Safe' or 'Type B' should be OK.

I hope you are successful and get lots of good use out of this project, please let me know.

Rich

Comments

[chipscola]

Aw dude I just finished. Its working! I need 2 extra male/male Kables And Comp., Laptop and Cellphone etc are hooked up!
Totally doable!

Thank you so much for uploading! :)

[richfiddler11]

Hmmm... sounds like a very interesting project (with a potentially annoying sound :) ). Do you mind if I ask what the goal is? Sounds like you're experimenting with analog synthesizer principles? Trying to drive away rodents? (sorry ;^)

Putting that aside, yes, if you have 3 existing devices that  output the sounds you state above, you could definitely mix them and feed the output into a PC sound card line-in/mic input. Because the circuit is passive it is very quiet electronically and well shielded.

An easier way to prototype and experiment with this type of thing would be to get Audacity from http://audacity.sourceforge.net/ . Audacity is a free, open-source wave file editor (runs on PC, Mac and Linux).

In audacity,  you can create multiple tracks which can be either recorded or tones generated by the program. Then you can mix them to your heart's content and even see (and hear of course) what the resulting waveforms look like.

So if your A, B and C devices already exist, you could record them each to a mono track and mix them. If they don't exist, you could generate the tones. You would probably have to do the rhythms manually by inserting silences every so often. Audacity is not really that sophisticated on the tone generation side, but there are tons of free synthesis applications out there.

Good luck,

Rich

[Keystone88]

Hi Richfiddler11,

My apology that I seemed exaggerate something~. Goal is the same to what you targeted. I have car-navigator of which speaker is out of order anymore so that I need to connect it to the car AUX input together with homemade karaoke system.

I already have voice-pass filter circuit for my mp3 player together with echo-mic connected without resistors added like your device. The mixed sound without resistors is not good as you know. This time my goal is nothing but to save some money for commercial mixer.

I just wanna check ur device. A, B and C are pure sounds of Piano key A (440Hz beep sound), B and C. By feeding pure beeps within narrow frequency bends(440Hz +or- 2Hz? , 493.9Hz and 523.3Hz === each one row or line of frequency bend), I would like to see how accurately your mixer could make pure 3 rows of lines. If your device is not as good as commercial mixer ( i don't know how good the commercial mixer can make the mixture, either), the result frequency spectrum would not look like 3 rows but distorted or noise induced lines, that is, I'd rather have to spend some money to buy commercial mixer to enjoy good sound in my car.

Thanks for Audacity. Chk the frequency analyzer here: http://relisoft.com/Freeware/index.htm . You can SEE the sound in spectral display. Simply say "Do, Re, Mi, Fa, Sol, Ra, Si, Do, etc...". In the spectral frequency display, you could see the frequency bends used in making each sound. If you provide pure note A sound(440Hz), it will make pure horizontal line near 440Hz height in the display. I will build your device and will see the result of the mixture of 3 feedings.

Thank you.

[Keystone88]

Hi richfiddler11,

Your instruction is unbelievably wonderful and simple for what I wanted to make.

I have a question. See my concept. There're 3 channels (mono).
Ch#1 has only one pitch with various beats or rhythms. Note = A 440Hz.
Ch#2 also has only one note B(493.9Hz) with various and random beats.
Ch#3 also has only one note C(523.3Hz) with continuous beeping or random beats.
Each ch doesn't include any noise at all originally.

Put Ch#1#2#3 into your mixer. And connect PC's REC input with your mixer's output to record the mixture of Ch#1#2#3.

What the .wav's spectral frequency display looks like? I expect very sharp 3 rows of solid or dotted lines. Is it right? I would like to know if your device can make noise-proof mixed result.

Thank you for your post.